Method of manufacturing ribbed steel rods



Dnc. 10, 1957 H. HOFF Erm.V 2,816,052

" METHOD OF" MANUFACTURING RIBBED STEEL RODS 3 Sheets-Sheet 1 2 w h I m/m M w J Lm L ,n H um .Tawl 6 1|cILm m m 6. n IMA m w H ///////////wFiled Nv. 8. 1954 H. Hor-'F :TAL

METHOD OF MANUFACTURING RIBBED STEEL RODS 3 Sheets-Sheet 3 Dec. 10, 1957Filed Nov. 8. 1954 Nrs/vives;

Hubcr" Hof- .'Gtorg Fischer United States Patent METHOD F MANUFACTURINGRIBBED STEEL RODS Hubert Hoff, Dortmund, and Georg Fischer, Schwerte,

Germany, assignors to Hoesch-Westfalenhntte Aktiengesellschaft,Dortmund, Germany Application November 8, 1954, Serial No. 467,602

Claims priority, application Germany November 7, 1953 14 Claims. (Cl.148-12) The present invention relates to a method of manufacturingribbed steel rods, and more particularly to a method of manufacturingribbed steel rods used for reinforcing of concrete.

It is known that the elastic limit or yield point and the strength ofsteel can be increased by cold deformation, and that the breakingelongation, which is considerably reduced by cold deformation, can beimproved by subsequent tempering without causing considerable reductionin the elastic limit or strength of the steel due to the tempering.However, it has been found that objects made in accordance with thisprocess, and especially objects made of Thomas steel, show brittlenessin spite of improved elongation quality wherever sharp notches orindentations cause tension peaks under conditions of stress.

For instance, concrete reinforcing ribbed steel rods of Thomas steel,manufactured as described above and belonging to group IIIb and IVbaccording to the German standard DIN 1045 and having the followingproperties:

are not usable, because breaks due to brittleness may already occurduring bending and positioning of the reinforcing rods at the buildinglocation. Hot-rolled Thomas rib steel while possessing greater strengthalso does not have suicient tenacity.

It is also known to use steel rods formed with two longitudinal ribs orwith two longitudinal ribs and interposed transversal or oblique ribsand to cold-twist these rods for use as concrete reinforcements. Thesetwisted rods are preferably made with a pitch of -12 times the roddiameter, especially when Thomas steel is used. Increased twisting,especially reducing the pitch below 8 times the diameter of the rodcauses the breaking tension to fall below permissible limits. Making ofhighly twisted reinforcement rods and tempering the same has not beenpractical, since it was not known that by doing so considerableimprovements could be achieved not only in regard to the values of thebreaking tension but also in regard to the ductility of the rod.

lt is an object of the present invention to provide a method for themanufacture of ribbed steel rods which overcomes all of theabove-mentioned disadvantages.

It is another object of the present invention to provide a method forthe manufacture of ribbed steel rods which have great ductility, highbreaking elongation and are less apt to develop cracks and fissuresunder the strains and stresses connected with their use as concretereinforcements.

It is still another object of the present invention to provide a methodfor themanufacture of highly twisted ribbed steel rods which have highbreaking tension and do not show a tendency towards developing cracksand fissures.

lt is a further object of the present invention to provide a method forthe manufacture of ribbed steel rods for reinforcing concrete which inaddition to the aforementioned advantages have a high degree of notchimpact tenacity.

Other objects and advantages of the present invention will be apparentfrom a further reading of the specification.

With the above objects in view the present invention mainly consists ina method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod and deforming the' sameso as to reduce its dimensions in one cross-sectional direction by atleast 30%, thereafter tempering the cold-rolled deformed steel rod at atemperature ranging between 450 and 600 Centigrade for at least l5minutes, and forming ribs on the steel rod not less than 15 minutesbefore termination of the tempering whereby the cold-rolled deformedsteel rod with the ribs thereon is tempered for at least 15 minutes atthe indicated temperature.

More particularly the method of the present invention comprises thesteps of cold rolling a steel rod having an oblong cross section anddeforming the same so as to reduce its dimensions in one cross sectionaldirection by at least 30% and to form a circular cross section; formingstraight longitudinal ribs on the steel rod equally spaced from eachother in circumferential direction, twisting the so-formed rod lso thateach of the straight longitudinal ribs is deformed into a helical rib,the distance of the thus-formed helical ribs from each other being equalto about 0.7 time the diameter of the deformed steel rod and the pitchof the heli-cal ribs being less than 6 times the diameter of thedeformed steel rod, and thereafter tempering the steel rod at atemperature ranging between 450 and 600 centigrade for at lesat l5minutes.

According to the present invention the cold rolling of Steel rods isperformed in such a way as to achieve a decrease in the thicknesses ofthe rods equal to a deformation of at least 30% in the area between theribs. The tempering is performed at a temperature of between 450 and 600C. for a sufficiently long period of time so as to obtain increasingvalues for notch impact resistance without appreciable decrease in theelastic limit and strength of the steel rod.

The fillet-shaped area -connecting the ribs with the steel rod is inaccordance with the present invention exposed to even greaterdeformation, preferably ranging between 30 and 60%. Due to the increaseddeformation recrystallization takes place in this area during tempering,and consequently stresses which otherwise might cause formation ofcracks are relieved. This is achieved by forming the ribs in such a waythat the cross-section of the area connecting the ribs with the steelrod forms an arc of very small radius.

The ribs may be rolled onto the rod either cold or at temperingtemperatures.

The rod prior to the cold-rolling process of the present invention mayhave various cross-sections such as for instance oblong, rectangular orcircular, and may have been produced by a hot or cold rolling process.It is then cold-rolled and deformed to the desired cross-section. Forinstance, a rod of square cross-section is cold-rolled into a rod ofelongated rectangular cross-section or vice versa; a rod of ovallcross-section is cold-rolled into a inite range of temperature.

rod of circular cross-section, or a rod of circular crosssection iscold-rolled to a rod having a cross-section of oval shape, both havingtransversal ribs. The crosssection of the rod may be changed bycold-rolling in accordance with the present invention in any desiredway, provided that a deformation of at least takes place during thecold-rolling. For` instance, the rod can be cold-rolled along two axesperpendicular to each other in order to achieve deformation of at least30% and to form at the same time ribs on the surface of the rod.

It has now been found that the tenacity or ductility of cold-rolled andtempered steel, especially Thomas steel, can only then be improvedwithout considerable loss of strength and reduction of the elastic limitor yield point, when the cold deformation exceeds a certain minimumvalue and when the tempering takes place within a def- For thecold-rolling, depending upon quality and condition of the material, areduction in thickness of at least 30% is required. This minimumreduction value is not determined by the shape of the steel rod or bythe required values for the yield point or tensile strength but by thetenacity and ductility required of high grade concrete reinforcing rods.

In accordance with the present invention, the tempering, followingdeformation of the rod in excess of the above stated minimum, has to becarried out within the temperature range of 450 to 600J centigrade, inorder to achieve a considerable increase in tenacity and ductilityconcurrent with a high elastic limit and great strength of the steelrod.

Tempering at a temperature below 450 centigrade tends to improve onlythe elastic limit which has been reduced during cold deformation,however, it does not appreciably change the notch impact tenacity instress areas such as the fillet or notch-like areas connecting the ribswith the main body of the rod.

On the other hand, if during tempering the temperature increases above alimit of from 580 to 600 centigrade, a decrease in strength occurs dueto recrystallization taking1 place throughout the entire cross-sectionof the steel ro Above the lower limit of cold deformation and within thetemperature range provided by the present invention, the notch impacttenacity increases with increasing deformation and higher temperingtemperatures, whereby the elastic limit or yield point and the strengthof the steel rod continue to increase with Vthe increase in'deformationcausing reduction ofthe thickness of the rod in one direction. In orderto achieve a high notch impact tenacity it is therefore advisable inaccordance with the present invention to obtain the highest possibledegree of cold deformation and to temper at high temperatures which,however, must not exceed'the upper limit of between 580 and 600centigrade.

The usual tempering time of between 2 and 5 minutes is not suflcient toachieve the desired increase in notch impact tenacity. In accordancewith the present invention the tempering process has to extend over aperiod of from 15 to 90 minutes.

By working in accordance with the method of the present invention asabove described, especially the notch impact tenacity of cold deformedsoft Thomas steel is considerably improved. By applying for instance, avery high degree of cold deformation, corresponding to a reduction inthickness of about 60%, followed by suitable tempering, for instance ofone hour at 500 centigrade, it is possible to approximately regain thenotch impact tenacity of the hot-rolled initial material, while at thesame time increasing the elastic limit to about 2.5 times its initialvalue.

The process of the presentinvention is especially suitable for themanufacture of ribbed concrete reinforcing rods belonging to groups IIIband IVbof the German standards DIN 1045 'which were described furtherabove.

It is important in' 'thiscaseto a'chieve 'not'only an 'increase in thenotch impact tenacity together with a high degree of cold deformation,but also in addition to reduce considerably the notch effect in the areaconnecting the ribs with the main body of the steel rod. This is done byrecrystallization of the material in this area. In ordcr to achieve thisresult it is necessary to increase the deformation in the areaconnecting the ribs with the main body of the steel rod to aconsiderably higher value than the deformation of the remainder of thecross-section of the steel rod; so that during temperingrecrystallization and relieving of stress occurs only in this particulararea, while the strength of the remainder of the steel rod remainssubstantially unchanged at the level attained by thc cold deformationprocess. Due to the relieving of strain of the material in this area, ahigh capacity for deformation is obtained which is necessary for aneffective reduction of the stress peaks. In this Way it is possible tomanufacture from soft Thomas steel, for instance, crossribbed concretereinforcing rods which conform with the German standards according toDIN 1045 for concrete reinforcements of steel of the groups Hlb and IVband which in comparison with concrete reinforcement rods made fromThomas steel in accordance with other methods show considerably betterqualities in regard to tenacity and resistance against formation ofcracks, while being of equal strength.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

Fig. 1 is a graph showing the stretch limit of steel under temperingconditions in accordance with the present invention, in relation to thedegree of cold deformation;

Fig. 2 is a graph showing the impact tenacity of steel under temperingconditions in accordance with the present invention, in relation to thedegree of cold deformation;

Fig. 3 is a cross-sectional view of a cylindrical steel rod prior todeformation in accordance with the present invention; f

Fig. 4 is a cross-sectional view of the steel rod shown in Fig. 3, afterdeformation;

Fig. 5 is a plan view of the steel rod shown in Fig. 4;

Fig. 6 is a cross-sectional view of an oval steel rod prior todeformation in accordance with the present invention;

Fig. 7 is a cross-sectional View of the steel rod shown in Fig. 6, afterdeformation;

Fig. 8 is a plan view of the steel rod shown in'Fig. 7;

Fig. 9 is a cross-sectional view of a steel rod provided withlongitudinal ribs in accordance with the present invention; and

' Fig. 10 is a plan view of the steel rod shown in Fig. 9 after twistingof the same.

The relationship between the reduction of thickness and the elasticlimit at tempering temperatures of 450 and 500 centigrade and at atempering time of one hour is shown in Fig. 1, while Fig. 2 shows thechange in the notch impact tenacity under deformation and temperingconditions identical with those of Fig. 1. The tempering time depends onthe size of the cross-section of the steel rod.

As graphically illustrated in Figs. 1 and 2, the elastic limit increaseswith the increase in cold deformation, while the notch impact tenacitydecreases upon application of a small degree of cold deformation andonly starts to increase when the degree of cold deformation reachesvalues approaching 40%. Upon further increase in the cold deformation,up to between 50 and 60%, the notch impact tenacity shows a very highrate of increase.

"Figs 1 and 2 ygraphically illustrate why in accordance with the presentinvention the area connecting the ribs with the main body of the rod hasto be deformed to a higher degree than the other portions of the ribbedsteel rod. As shown in these figures a sufficiently high value for theelastic limit is obtained when deformation exceeds 30%, whiledeformation between 40 and 60% in the critical area between the ribs andthe rod is needed to obtain a satisfactory increase in the impacttenacity.

This is utilized in accordance with the present invention, in regard totwisted ribbed steel rods for concrete reinforcements, and done bytwisting the ribbed rods to such an extent that the pitch of the helicalribs formed from originally longitudinal ribs by twisting of the steelrod, is below six times the maximum dimension of the cross-section ofthe rod, preferably between two and four times the maximum dimension. Iffor example a ribbed rod of circular cross-section having straightlongitudinal ribs equally spaced from each other in circumferentialdirection is used, the twisting in accordance with the present inventionis to be carried out to such an extent that the pitch of the helicalribs formed thereby is smaller than six times the diameter of said rodand preferably lies between two and four times that diameter. Twistingof the steel rod to the extent indicated above and subsequent temperingfor a period of between and 90 minutes, depending on the size of thecross-section of the ribbed rods, at a temperature of between 450 and600 C. will cause the notch impact tenacity to increase again, withoutappreciable reduction of the high elastic limit and strength achieved bythe cold twisting of the rod.

According to this process of the present invention an improvement in themechanical characteristics of the steel rods is achieved and the desiredvalues in respect to notch impact tenacity and elastic limit arereached.

Furthermore, a new and considerable advantage is achieved for having thehelical ribs, formed from longitudinal ribs by twisting of the steelrod, arranged at such slope as to show a certain similarity with rodshaving transversal ribs. As it is known, transversal ribs on concretereinforcing rods possess the extraordinary advantage of increasing theadherence of the concrete to the reinforcing rod. The steep helical ribsof conventionally twisted reinforcing rods provide a somewhat betteradherence than smooth rib-less reinforcing rods. However, longitudinalforces acting on the embedded reinforcing rod create, in the case ofsteep helical ribs, a relatively large force component in the directionof the ribs and consequently the rod shows a certain tendency toseparate from the concrete by rotation. With reduced gradient of thehelical ribs this force component becomes smaller and consequently, inorder to prevent movement of the reinforcing rod relative to theconcrete, it is of great advantage to increase the twisting of the rodin accordance with the present invention.

Conventional reinforcing rods with transversal ribs have the ribsarranged in a distance from each other which is about equal to 0.7 timesthe diameter or maximum dimension of the cross-section of thereinforcing rod, in order to enforce a desirable formation of cracks inthe concrete; that is to obtain as many cracks as possible, which are,consequently, of small width. The same eect can be achieved by areinforcing rod which is strongly twisted in accordance with the presentinvention, if the number of longitudinal ribs which are equally spacedfrom each other in circumferential direction is chosen in relation tothe pitch of the helical ribs obtained after twisting in such a way thatthe distance between adjoining ribs deformed by twisting into helicalribs, amounts to approximately 0.7 times the diameter or maximumydimension of the cross-section of the steel rod. This is achieved byarranging, for instance, four equally spaced ribs around thecircumference of the rod and twisting to an extent that the pitch of thehelical ribs amounts to three times the diameter of the rod, or if, forinstance, the pitch is to be four times the diameter, six ribs have "6to be arranged around the circumference of the rod to achieve the sameresult.

It is advantageous to use as raw material for the forming of concretereinforcing steel rods, in accordance with the method of the presentinvention, a Thomas steel which -has been produced with the addition ofoxygen to the air blast. Due to the enrichment in oxygen content, thenitrogen content of the steel is reduced to values below those found inregular Thomas steel. This low nitrogen-content steel is especiallysuitable to withstand the high twisting operation performed inaccordance with the present invention. Preferably the nitrogen contentof the steel is kept below 0.012%. Obviously different types of Thomassteel in which the nitrogen content has been lowered by variousprocesses can also be used, as well as open hearth steel.

Referring now again to the drawings, Figs. 3, 4 and 5 show a steel rodof initially circular cross-section before and after deformation inaccordance with the present invention. The steel rod blank having adiameter rz as shown in Fig. 3 is deformed in the direction of diametera to an extent exceeding 30%. As shown in Fig. 4, diameter a has beenreduced to diameter a1 for the main body of the deformed steel rod, andto diameter a2 for the ribs rolled on the main body of the steel rod. InFig. 5, b indicates the fillet area connecting the ribs with the mainbody of the steel rod, which area in accordance with the presentinvention is deformed to a degree exceeding the degree of deformation ofthe steel rod, preferably to a degree of between 30 and 60%, and inwhich area recrystallization and release of stress is achieved duringthe subsequent tempering process.

Figs. 6, 7 and 8 show the deformation and formation of ribs on a steelrod blank of initially oval crosssection. The original steel rod has alongest axis c and a shortest axis d as shown in Fig. 6. The rod iscolddeformed so as to reduce the longest axis c to c1 for the main bodyof the steel rod and to c2 for the ribs rolled on the main body. Thisreduction in length of the longest axis of the original steel rod, asshown in Fig. 7, exceeds 30%. As shown in Fig. 8 two longitudinal ribsand a plurality of transversal ribs were rolled on the main body of thesteel rod. The llet areas connecting the ribs with the main body of therod which in accordance with the present invention have been deformed toa degree exceeding the deformation of the main body of the rod areindicated in Fig. 8 by the letter e. The difference in the degree ofdeformation between these areas e and the main body of the steel rod issuch that upon tempering at temperatures between 450 and 600 for aperiod of time of l5 to 90 minutes, recrystallization takes place in theareas e only and not in the main body of the steel rod. The upper limitof tempering temperature is chosen in accordance with the degrees ofdeformation actually applied, but in any event not to exceed 600 C. soas to prevent recrystallization in the main body of the steel rod.

In the cross-sectional view shown in Fig. 9 of a deformed steel rodhaving straight longitudinal ribs equally spaced from each other incircumferential direction, the areas of greater deformation connectingthe ribs with the main body of the steel rod are indicated by the letterf.

Fig. l0 shows a steel rod having helical ribs formed on its surface bythe process of twisting a steel rod having longitudinal ribs equallyspaced from each other in circumferential direction. lt specificallyshows the relationship between the diameter g of the steel rod, thedistance of adjoining helical ribs from each other, and the pitch of thehelical ribs. In the illustrated embodiment shown in Fig. l0, thedistance between adjoining helical ribs is equal to 0.7 times thediameter of the steel rod and the pitch of the helical ribs equals 4times the diameter of the steel rod. The high twist of the steel rod andthe consequently relatively small pitch of the ribs causes provided withtransversal ribs.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that'others canby applying current knowledgereadily adapt itfor various applications without omitting features that,from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations shouldaud are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured vby Letters Patent is:

l. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel and deforming the same so as to reduce its dimension in onecross-sectional direction by at least 40%; thereafter tempering saidcoldrolled deformed steel rod at a temperature ranging between 450 and600 centigrade for at least l5 minutes, and forming ribs on said steelrod not less than 15 minutes before termination of said tempering sothat said coldrolled deformed steel rod with said ribs thereon istempered for at least 15 minutes at the indicated temperature, whereby aribbed steel rod of high elastic` limit and high notch impact tenacityis formed.

2. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod and deforming the sameso as to reduce its a steel rod consisting of Thomas steel and deformingthe same so as to reduce its dimensions in one cross-sectional directionby at least 40%; thereafter tempering said coldrolled deformed steel rodat a temperature of approximately 500 centigrade for between l5 and 90minutes, and forming ribs on said steel rods not less than l5 minutesbefore termination of said tempering-so that said cold-rolled deformedsteel rod with said ribs thereon is` tempered for at least l5 minutes-at the indicated 'ternperature, whereby a ribbed steel rod of highelastic limit and high notch impact tenacity is formed.

4. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel andl deforming the same so as to reduce its dimensions in onecross-sectional direction by at least 40%; thereafter tempering saidcoldrolled deformed steel rod at a temperature ranging between 450 and600 centigrade for at least 15 minutes, and forming ribs on said steelrod not less than l5 minutes before termination of said tempering,thereby deforming the area connecting said ribs with said steel rod to adegree of between 40% and 60% thus causing recrystallization andrelieving of stress in said area, and tempering said cold-rolleddeformed steel rod with the ribs thereon for at least l5 minutes at theindicated temperature, whereby a ribbed steel rod of high elastic limitand high notch impact tenacity is formed.

5. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rollingl a steel rod 'consisting of Thomassteel and deforming thev tween 450 and 600 centigrade forat least 15minutesf forming str-aight. longitudinalribs-on said steel'rodgand'twisting the so formed 'rod so that-each of said'straight` fcatedtemperature, whereby a ribbed steel rod ofhigh elastic limit andhigh notch impact tenacity is formed.

6. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consistingv of Thomassteel and deforming the same so as'toreduce its dimensions in onecross-sectional direction by at least 40%; thereafter tempering saidcoldrolled deformed steel rod at a temperature ranging between 450" and600 centigrade for at least 15 minutes, forming straight longtudinalribs on said steel rod; and

`twisting the so formed rod so that each of said straight longitudinalribs is deformed into a helical rib, having a pitch of less than sixtimes the maximum dimension of the cross section of saiddeformed steelrod, not less than l5'minutes before termination of said tempering sothat said cold-rolled deformed steel rod with said ribs thereon istempered for at least 15 minutes at the indicated temperature, whereby aribbed steel rod of high elastic limit and high notch impact tenacity isformed.

7. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel and deforming the same so as to reduce its dimensions in onecross-sectional direction by at least-40%; thereafter tempering saidcoldrolled deformed steel rod at a temperature ranging between 450 and600 centigrade for at least 15 minutes, forming straight longitudinalribs on said steel rod; and twisting the so formed rod so that each ofsaid straight longitudinal ribs is deformed into a helical rib, having apitch of between two and six times the maximum dimension -of the crosssection of said deformed steel rod, not less than 15 minutes beforetermination of said tempering so that said cold-rolled deformed steelrod with said ribs thereon is ltempered for at least l5 minutes at theindicated temperature, whereby a ribbed steel rod of high elastic limitand high notch impact tenacity is formed.

8. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel and deforming the same so as to reduce its dimensions in onecross-sectional direction by at least 40%; forming straight longitudinalribs on said steel rod equally spaced from each other in circumferentialdirection; twisting the so-formed rod so that each'of vsaid straightlongitudinal ribs is deformed into'a helical rib the distance of thethus formed helical ribs from each other being about 0.7 times themaximum dimension'of the cross section of said deformed steel rod; andthereafter tempering said steel rod at a temperature ranging between 450and 600 centigrade for at least 15 minutes, whereby by a ribbed steelrod of high elastic limit and high notch impact tenacity is formed.

9; A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel of oblong cross section thereby deforming the same so as to reduceits dimensions in one cross-sectional direction by at least 40% and to.form a circular cross section; thereafter tempering said cold-rolleddeformed steel rod at a temperature ranging between 450 and 600centigrade for at least 15 minutes, and forming ribs on said steel rodnot less than l5 minutes before termination of said temperingV so thatsaid cold-rolled deformed steel rod with said ribs thereon is temperedfor at least l5 minutes at the indicated temperature, whereby a ribbedsteel rod of high elastic limit and high notch impact tenacity isformed.

10. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consistingof Thomassteel and deforming the same so as to reduce-its dimensions in onecross-sectional direction byat least 40%; forming-straight longitudinal'`ribs onv said steel-rodl equally spaced `from each other inocircumferential direction; twisting the so-formed rod so that each ofsaid straight longitudinal ribs is deformed into a helical rib, thepitch of said helical ribs being less than 6 times the maximum dimensionof the cross section of said deformed steel rod; and thereaftertempering said steel rod at a temperature ranging between 450 and 600centigrade for at least 15 minutes, whereby a ribbed steel rod of highelastic limit and high notch impact tenacity is formed.

11. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel having an oblong cross section and deforming the same so as toreduce its dimensions in one cross sectional direction by at least 40%and to form a circular cross section; forming straight longitudinal ribson said steel rod equally spaced from each other in circumferentialdirection; twisting the soformed rod so that each of said straightlongitudinal ribs is deformed into a helical rib, the distance of thethusformed helical ribs from each other being equal to about 0.7 timesthe diameter of said deformed steel rod and the pitch of said helicalribs being less than 6 times the diameter of said deformed steel rod;and thereafter tempering said steel rod at a temperature ranging between450 and 600 centigrade for at least 15 minutes, whereby a ribbed steelrod of high elastic limit and high notch impact tenacity is formed.

12. A method of manufacuring ribbed steel rods made of Thomas steelhaving a nitrogen content of not more than 0.012% for reinforcingconcrete comprising the steps of cold-rolling a steel rod consisting ofThomas steel having a nitrogen content of not more than 0.012% anddeforming the same so as to reduce its dimensions in one cross-sectionaldirection by at least 40%; thereafter tempering said cold-rolleddeformed steel rod at a tempcrature ranging between 450 and 600centigrade for at least 15 minutes, and forming ribs on said steel rodnot less than 15 minutes before termination of said tempering so thatsaid cold-rolled deformed steel rod with said ribs 10 thereon istempered for at least 15 minutes at the indicated temperature, whereby aribbed steel rod of high elastic limit and high notch impact tenacity isformed.

13. A method of manufacuring ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel in two directions normal to each other and deforming the same soas to reduce its dimensions in one cross-sectional direction by at leastand to form a rectangular cross-section; thereafter tempering saidcold-rolled deformed steel rod at a temperature ranging between 450 and600 centigrade for at least l5 minutes, and forming ribs on said steelrod not less than 15 minutes before termination of said tempering sothat said cold-rolled deformed steel rod with said ribs thereon istempered for at least 15 minutes at the indicated temperature, whereby aribbed steel rod of high elastic limit and high notch impact tenacity isformed.

14. A method of manufacturing ribbed steel rods for reinforcing concretecomprising the steps of cold-rolling a steel rod consisting of Thomassteel in two directions normal to each other and deforming the same soas to reduce its dimensions in one cross-sectional direction by at least40% and to form a rectangular cross-section; thereafter tempering saidcold-rolled deformed steel rod at a temperature ranging between 450 and600 centigrade for at least 15 minutes, and forming transversal ribs onat least two opposite surfaces of said steel rod not less than 15minutes before termination of said tempering so that said cold-rolleddeformed steel rod with said ribs thereon is tempered for at least 15minutes at the indicated temperature, whereby a ribbed steel rod of highelastic limit and high notch impact tenacity is formed.

644,598 Great Britain Oct. 11, 1950

1. A METHOD OF MANUFACTURING RIBBED STEEL RODS FOR REINFORCING CONCRETECOMPRISING THE STEPS OF COLD-ROLLING A STEEL ROD CONSISTING OF THOMASSTEEL AND DEFORMING THE SAME SO AS TO REDUCE ITS DIMENSION IN ONECROSS-SECTIONAL DIRECTION BY AT LEAST 40%; THEREAFTER TEMPERING SAIDCOLDROLLED DEFORMED STEEL ROD AT A TEMPERATURE RANGING BETWEEN 450* AND600* CENTIGRADE FOR AT LEAST 15 MINUTES, AND FORMING RIBS ON SAID STEELROD NOT LESS THAN 15 MINUTES BEFORE TERMINATION OF SAID TEMPERING SOTHAT SAID COLDROLLED DEFORMED STEEL ROD WITH SAID RIBS THEREON ISTEMPERED FOR AT LEAST 15 MINUTES AT THE INDICATED TEMPERATURE, WHEREBY ARIBBED STEEL ROD OF HIGH ELASTIC LIMIT AND HIGH NOTCH IMPACT TENACITY ISFORMED.